Flowing in the Past: Evidence of Water on Mars Quiz

A delta is a fan shaped geological feature created when a river enters a standing body of water like a lake or ocean. As the water slows down it drops all the sediment it was carrying creating layers of rock. For scientists these layers are like the pages of a history book potentially holding fossils of anything that lived in the water.

On Earth the air pressure is high enough to keep water in a liquid state but on Mars the pressure is so low that liquid water would instantly boil away or freeze. This means that while we see evidence of past water any water on the surface today exists only as ice or occasional salty streaks that vanish almost instantly.

Hematite is an iron rich mineral that typically forms in watery environments such as hot springs or standing pools of water. When the Opportunity rover discovered small spherical grains of hematite nicknamed blueberries on the Martian surface it provided definitive chemical proof that the area had once been soaked in liquid water for a long period.

Recurring Slope Lineae are dark streaks that appear on Martian hillsides during the warmest parts of the year and fade when temperatures drop. Scientists believe these are caused by brines which are flows of extremely salty water. The salt acts as an antifreeze allowing the water to stay liquid momentarily even in the freezing Martian environment.

While Mars looks like a dry dusty desert it actually contains a massive amount of water trapped as ice at the North and South poles. These polar caps are made of a mixture of water ice and dry ice which is frozen carbon dioxide. If all the water ice at the poles melted it could cover the entire planet in an ocean.

The Curiosity rover discovered fine grained sedimentary rocks known as mudstone which only form when very small particles of silt and clay settle at the bottom of a quiet lake. This discovery in Gale Crater proved that a lake existed there for millions of years providing a stable environment where microscopic life could have potentially thrived.

Salt is a critical component for the possibility of liquid water on Mars because it lowers the freezing point of the liquid. Just as we put salt on icy roads in the winter to melt them the natural salts in Martian soil allow water to remain liquid at temperatures far below the normal freezing point of pure water.

Outflow channels are massive wide paths carved into the Martian surface that look remarkably similar to areas on Earth where giant floods have occurred. These features suggest that in the distant past huge amounts of water were suddenly released from underground rushing across the landscape with enough force to move giant boulders and carve out deep valleys.

When the Phoenix lander used its robotic arm to dig a shallow trench in the Martian soil it uncovered bright white patches that completely disappeared after a few days. Since the material did not melt into a liquid scientists concluded it was water ice that had sublimated meaning it turned directly from a solid into a gas.

Billions of years ago Mars had a much thicker atmosphere that could trap heat creating a greenhouse effect similar to Earth. This allowed the planet to be warm enough for rain to fall and rivers to flow. Over time the planet lost its atmosphere to space causing it to transform into the cold dry desert we see today.

Gullies and stream channels are erosional features that show a distinct branching pattern which on Earth is exclusively caused by flowing liquid. By comparing satellite images of these Martian features to river systems on Earth geologists can determine exactly how much water was needed to move the soil and rocks to create such deep and complex paths.

Sublimation is a unique process where a substance skips the liquid phase entirely moving from a solid to a gas. On Mars because the atmospheric pressure is so incredibly low water ice and frozen carbon dioxide do not melt when they get warm instead they boil directly into the thin air which explains why surface ice disappears so quickly.

Clay minerals or phyllosilicates are water loving minerals that are formed through the long term chemical weathering of rocks by liquid water. Finding large deposits of clay in Martian craters tells scientists that water did not just rush by in a flood it must have sat there in a lake or pool for thousands of years to change the chemistry of the rocks.

The Warm and Wet hypothesis is the leading theory among planetary scientists to describe early Mars. It suggests that the first billion years of the planet history featured a climate with a stable water cycle. This is the most important time period for astrobiology as it represents the best window of opportunity for life to have started.

Layered sediments are often found in the basins of Martian craters suggesting that these craters once acted as giant bowls that held ancient lakes. Each layer of sediment represents a different period of time allowing rovers like Perseverance to read the history of the water levels and the environmental conditions that existed billions of years ago.

Water ice is surprisingly common on Mars but it is rarely visible because it is usually buried under a layer of red dust or mixed with frozen carbon dioxide. Aside from the poles large sheets of ice have been detected just beneath the surface in the mid latitude regions which could be a vital resource for future human explorers.

The Perseverance rover is currently exploring a massive ancient river delta inside Jezero Crater. This site was chosen specifically because deltas are excellent at preserving organic molecules. The rover is drilling rock cores from these watery sediments which will eventually be brought back to Earth by a future mission to be analyzed for signs of life.

Gullies on the walls of Martian craters often show evidence of alcoves at the top and fans of debris at the bottom. These patterns are characteristic of liquid flow rather than dry landslides. Their presence suggests that even in more recent Martian history small amounts of water may have occasionally melted and flowed down steep slopes.

It is important to distinguish between water ice and dry ice. While both exist on Mars dry ice is what makes up the majority of the seasonal frost and a large part of the polar caps. Water ice is more permanent and is the primary target for scientists looking for signs of habitability and ancient biological life.

The primary reason Mars lost its liquid water is because it lost its global magnetic field. Without that protection the solar wind a stream of charged particles from the sun stripped away the planet thick atmosphere. As the air became thinner the pressure dropped and the planet cooled down causing the water to either freeze or escape into space.